How to allocate multple activities to one resource

I cannot seem to be able to do this.  When I try it opens up a new tab everytime I press CTRL or SHIFT or the combination.  Would you know why this is happening for me?

You must activate multiple update mode
 

It was possible.  I know this is bizarre, me a user, telling you, the programmer, that it was possible.  It was.  Maybe I am incorrectly using the terminology.  However I know that in version 8, I would be able to select multiple activities, then click on the option to change specific fields and one of those fields was to change the resource of who was working on the particular activity.  I know this was possible as I would do it regularly.  I hope this explanation may remind you of the feature/function.

Yes, it was possible to change the "responsible" of an activity, but not to change the assignments of resources to the activity.
And it is still possible with multiple update.
And now with Assignment screen, it is also possible to change multiple assignements in one click, with only constraint that name of activity is not displayed, you must deal with its id..